A second South Korean hostage has been found dead in central Afghanistan, as the Taliban threatened to kill more of the remaining 21 captives by tomorrow.

Police discovered the man's bloodstained body on a roadside this morning in the village of Arizo Kalley, six miles west of Ghazni city, in the Andar district.

The South Korean foreign ministry identified him as 29-year-old Shim Sung-min, a former information technology worker who volunteered with a church group on an aid mission to Afghanistan.

He appeared to have a gunshot wound to the right temple.

A purported Taliban spokesman claimed he was killed last night because the Afghan government failed to meet its demand for the release of Taliban prisoners.

Qari Yousef Ahmadi, repeated the group's demand for an exchange of Taliban prisoners for the Christian volunteers.

The Taliban kidnapped 23 South Koreans travelling on a bus through Ghazni province on the main road between Kabul and Kandahar on July 19. It's the largest group of foreign hostages taken in Afghanistan since the 2001 US-led invasion.

"The Kabul and Korean governments are lying and cheating. They did not meet their promise of releasing Taliban prisoners," Mr Ahmadi said by phone from an undisclosed location.

He also set a new deadline for potentially all of the remaining hostages.

"If the Kabul government does not release the Taliban prisoners, then we will kill after 12 o'clock - we are going to kill Korean hostages," Mr Ahmadi said.

"It might be a man or a woman ... It might be one. It might be two, four. It might be all of them."

The Al-Jazeera television network, meanwhile, showed shaky footage of what it said was several South Korean hostages.

Some seven female hostages, heads veiled in accordance with the Islamic law enforced by the Taliban, were seen crouching in the dark, eyes closed or staring expressionless at the ground.

The hostages did not speak as the hand-held camera filmed them.

The Taliban has set several deadlines for the South Koreans' lives.

Last Wednesday, they killed their first hostage, a male leader of the group.

The body of pastor Bae Hyung-kyu arrived back in South Korea yesterday, where the families of the remaining hostages pleaded for their loved ones' release.

It's not clear if the Afghan government will consider meeting the Taliban's demand.

In March, President Hamid Karzai approved a deal that saw five captive Taliban fighters freed for the release of Italian reporter Daniele Mastrogiacomo.

Mr Karzai, who was criticised by the US and European government over the exchange, called the trade a one-off deal.

On Sunday, Mr Karzai and other Afghan officials tried to shame the Taliban into releasing the female captives by appealing to a tradition of cultural hospitality and chivalry. They called the kidnapping of women "un-Islamic."